The present invention relates to a three-dimensional light system for guidance of invasive procedures with computed tomogragraphic assisted instrument placement.
Prior to the development of computed tomography (C.T.) a variety of invasive procedures, such as tissue sampling, abcess drainage, etc., had been developed as alternatives to surgery where the lesion or target could be visualized fluoroscopically. These procedures generally involved a needle puncture and were applicable to lesions of lungs and bones where the natural contrast afforded good fluoroscopic visualization.
With the development of body computed tomography, the excellent portrayal of anatomic detail and tissue delineation in computed tomographic images permitted extension of the percutaneous techniques to various parts of the body, such as the abdomen, brain and other soft tissues.
With C.T. assisted instrument placement, the patient is removed from the C.T. gantry prior to undertaking the percutaneous procedures. Therefore, the scanners include narrow, accurate light beams for relating structures visualized in the computed tomographic cross-section images to the overlying body surface by reference to these mid-line and image slice level indicators. In the most common technique of referencing, a grid giving mid-line localization is displayed on the C.T. image. Lesion depth and distance from the mid-line are noted. The patient is positioned in the gantry at this slice level and the mid-line and transverse planes are marked on the patient's skin. The table is then withdrawn from the gantry and a skin mark is made at the slice level and at a distance from the mid-line selected as the entry point. From this point, a line gives direct access to the lesion if the estimated degree of angulation is correct. Rigid guides have been developed to improve precision of instrument placement in cranial and abdominal biopsies. These devices provide precise positioning of the biopsy needle. In the abdomen they restrict the biopsy path to a plane perpendicular to the axis of rotation of the gantry but allow for precise needle angulation within this plane. The disadvantage of restricting the needle position to the plane of the image is apparent and the use of trigonometric calculations has been proposed to permit longitudinal angulation in order to avoid structures overlying the target. This technique involves selection of the point of needle insertion, computation of the distance and path to the lesion and calculation of the exact angle of needle insertion. The needle is then inserted parallel to a straight edge held adjacent to the patient at the calculated angle.
The prior art techniques are useful, but are limited in their application because of imprecision and the time consumed for each procedure. Movement by the patient will lead to positioning errors with any system and the necessity for repeating the procedure. Patient motion is much more likely with long procedure times. The use of rigid guides makes it difficult to test for deflection of flexible needles and necessitates sterilization of such equipment. Lateral angular guidance with the prior art techniques is precise, but limited to the plane of the scan. Longitudinal angular guidance is not precise, involving a great deal of estimation, and there is no prior art provision for guidance at compound angles.